As it is known in the telecommunications art, dense wavelength division multiplexing (DWDM) is a technology that allows many wavelengths of light to travel along the same fiberoptic cable. Each of those wavelengths of light convey a stream of data that is filtered and decoded when it reaches an optical DWDM receiver. The DWDM technology significantly increases the amount of data that can be conveyed, at a single time, across a fiberoptic cable and hence is becoming highly utilized. Because the DWDM technology uses many different wavelengths of light, it has generated increasing interest in laser designs that can be tuned to any of those wavelengths. One such type of a laser is referred to as a tunable vertical cavity semiconductor laser (VCSEL).
In order to tune the output of a VCSEL, or other type of tunable laser, to a desired wavelength, a control circuit is manipulated such that the output ramps through a range of wavelengths. The output signal is monitored until it meets the desired wavelength criteria. At that time it is locked into place through further manipulation of the control circuit. In order to perform this tuning operation, a monitor is needed that has a wide dynamic range in both the power and wavelength domains. For example, in the case where a tunable laser wavelength is judged by the transmission through a wavelength dependent etalon to control the laser frequency within +/xe2x88x925 pm within the band of 100 nm (43 dB) and power within the band of 3 dB, a circuit having a dynamic range of at least 46 dB dynamic range is needed. It is also important to be able to monitor and control the wavelength and power of the VCSEL independently from each other across a wide environmental range of temperature and humidity.
Accordingly, a mechanism is needed for providing accurate and reliable wavelength and power measurements across wide dynamic operating ranges and wide dynamic environmental ranges.
In accordance with an aspect of the present invention, a system for determining the power and wavelength of an optical signal is provided. The system includes a pair of beam splitters and etalons with known transmission characteristics for receiving portions of the optical signal. Optical detectors generate electrical signals that are representative of the optical signal based upon the output of the etalons.
The electrical signals are received by a circuit that responsively generates a first output signal that is wavelength and power dependent and a second output signal that is wavelength dependent. A processor receives those signals and determines the wavelength from said second output signal and the power from the first output signal. The processor can do this by converting the electrical signal to a digital signal represented by characteristic equations and then solving those equations for the unknown values.
With such an embodiment, the characteristics of an unknown optical signal can be quickly determined.